Low-height articulated piston with skirt-overhanging guide portions on head

ABSTRACT

A two-part, low compression height, open-ended hollow skirt-type piston for internal combustion engines has a piston pin creating an articulated connection of the separate skirt and head parts. Guide portions (5) protruding axially in the direction of the piston axis provide lateral guidance and support of the piston head (1) in the piston-pin-axis direction. Each of the guide portions forms a gap with the nearby gudgeon pin boss (3). The gaps receive opposite parallel flat surfaces (4) of the skirt (2). The overhanging guide portions (5) have partly circular recesses permitting assembly of head and skirt with the gudgeon pin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to pistons especially pistons for internalcombustion engines.

2. Description of the Prior Art

Such pistons are known from Fed. German P.S. No. 2,351,994. A lowcompression height of the piston is achievable due to the fact that aring band of the piston head surrounds the skirt whereby the piston pincan be placed so far upwards in the piston skirt that the upper zone ofthe skirt bore receiving the piston pin can come to lie above thelowermost piston ring groove in the piston head.

In pistons of such formation it can occur that in specific cases,especially those where the lateral guidance of the connection rod takesplace in the piston head, with a low height of the cylindrical guideportion of the piston head there is no longer adequate lateral guidanceof the piston head in the direction of the axis of the piston pin.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a remedy of thisdefect.

According to the invention a piston comprises

a head part having a substantially cylindrical surface for slidingengagement within the inner cylindrical surface of a cylinder bore of aninteral combustion engine, gudgeon pin bosses extending from said headpart and spaced radially inwardly of said cylindrical surface, saidbosses having coaxial skirt part lying within a projection of thecylindrical surface and surrounding the gudgeon pin bosses, said skirtpart having axial bores therein coaxial with the bores of the bosses,and a gudgeon pin passing through the bores of said bosses and saidskirt to secure the skirt pasrt to the head part, the improvementcomprising the provision of

(a) two oppositely diposed flat surfaces of said skirt through whichpass the axial bores, said flat surfaces being substantially parallel toeach other and form chords of the projected cylindrical surface,defining with the latter segmental spaces, and

(b) guide portions integral with the head overhanging the exterior ofthe skirt by at least 10% of the longitudinal length of the skirt andlocated adjacent the opposite ends of the pin against said flat surfacesof said skirt, said guide portions extending in a direction away fromsaid head into the segmental spaces and having part circular recessespermitting passage of the gudgeon pin on assembly.

Also from Fed. German P.S. No. 1,291,955 a piston is already known inwhich the skirt extends out far above the pin bosses lying therebeneath.However this construction is not comparable with the constructionaccording to the invention, since piston head and skirt are not separatefrom one another.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of embodiment of the invention is illustrated in theaccompanying drawing, wherein:

FIG. 1 shows a piston partially in longitudinal section and partially inelevation,

FIG. 2 shows a lateral elevation of the piston,

FIG. 3 shows a section through the piston along the line III--III onFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The piston is composed of a piston head 1 and a piston skirt 2. Thesetwo parts are connected with one another by a piston pin (not shown)which engages in boss bores 3 of the piston head 1 and bores 4 in thepiston skirt 2. At opposite ends of the piston pin a guide portion 5 oneach side extends from the piston head 1 radially out beyond the skirt 2and extends in the direction of the piston axis approximately to thelevel of the piston pin axis. Openings for the passage of the piston pinare provided in these guide portions 5 which overhang the skirt 2. Theguide portions 5 extend beyond the lower edge of the head part in thedirection of the piston axis, at least 10%, preferably at least 20% andpreferably by about 40% of the length of the piston skirt 2. In thecircumferential direction the region in which the guide portion 5overlaps the skirt 2 measures about 60°, the portion 5 extending in eachcase symmetrically in relation to each side of the piston pin axis.

The skirt 2 adjacent opposite ends of the pin is of less diameter thanthe remainder circular parts of the skirt so as to provide two flatsurfaces engageable by the guide portions 5.

The two guide portions 5 lying at opposite ends of the piston pin andprotruding beyond the skirt 2 guarantee good lateral guidance of thepiston head 1. This is especially important in the lateral guidance ofthe connecting rod articulated to the piston, within the piston head 1.

The guide portions extend into segmental spaced formed between the flatsurfaces of the skirt and a projection of the substantially cylindricalsurface of the skirt.

I claim:
 1. An internal combustion engine piston comprising a head parthaving a substantially cylindrical surface for sliding engagement withinthe inner cylindrical surface of a cylinder bore of an internalcombustion engine; a pair of gudgeon pin bosses extending from said headpart and spaced radially inwardly of said cylindrical surface, saidbosses having coaxial bores formed therein to receive a gudgeon pin; apair of guide portions integral with the head and each located radiallyoutside and adjacent a respective gudgeon pin boss, each of said guideportions extending longitudinally in a direction away from said head andforming a respective gap between it and the respective gudgeon pin bossand each having a partly circular recess permitting passage of saidgudgeon pin during assembly; and a substantially annular skirt partlying within a projection of the cylindrical surface and surrounding thegudgeon pin bosses and passing through said gaps; said skirt part havinggudgeon pin bores therein coaxial with the bores of the bosses so thatwhen a gudgeon pin is assembled in said bosses it passed through saidgudgeon pin bores to secure the skirt part to said head part, and saidskirt part having a pair of oppositely disposed parallel flat surfaceslocated where said skirt part passes through said gaps, said gudgeon pinbores passing through respective ones of said flat surfaces.
 2. A pistonaccording to claim 1, wherein the guide portions extend longitudinallyof the piston by about 20% of the length of the skirt.
 3. A pistonaccording to claim 1, wherein the guide portions extend longitudinallyof the piston by about 40% of the length of the skirt.
 4. A pistonaccording to claim 3, wherein each of the guide portions extends aroundthe skirt over an angle of about 60°.